As related-art steering control devices, there are known steering control devices for generating a steering wheel return torque by a motor in order to improve steering wheel return characteristics at the time when a driver releases a steering wheel from his/her hand at low vehicle speed (for example, Patent Literatures 1 to 3).
In Patent Literature 1, polarity determination is performed to determine that a steering wheel is in a return state when a rotation direction of a motor and an input direction of a steering torque are different from each other, and whether or not to apply a return torque is selected. In order to prevent the occurrence of a phenomenon that a driver receives a force from the steering wheel in an unintended direction, namely, a so-called unintended steering of the steering wheel, which is caused even when the driver slightly returns the steering wheel in the steering-holding state (in the state in which the driver does not steer the steering wheel greatly during straight travel or the like), whether or not to apply the return torque is selected based on the magnitude of the steering torque.
In Patent Literature 2, the following configuration is proposed. A target steering angle for returning a steering wheel to a neutral position is set based on a steering angle and a vehicle speed, and an ideal target steering angular speed is set depending on a deviation between the target steering angle and the steering angle and on the vehicle speed. A target converging current is set based on a deviation between the target steering angular speed and a steering angular speed. Then, when a steering torque is near 0, it is determined that a driver is lightly touching the steering wheel with his/her hand or that the driver is releasing the steering wheel from his/her hand, and the target converging current is applied.
In Patent Literature 3, it is proposed to multiply a deviation between a target steering angular speed and a steering angular speed by a steering torque multiplication coefficient value, to thereby calculate a correction current value.
As described above, in the related-art steering control devices, in a region in which the steering torque is small, it is determined that the driver is lightly touching the steering wheel with his/her hand or that the driver is releasing the steering wheel from his/her hand, and the steering wheel return torque for improving the steering wheel return characteristics is applied. In contrast, in a region in which the steering torque is large, it is determined that the driver is holding and steering the steering wheel, and the application of the steering wheel return torque is stopped or suppressed.